A problem which exists in the art is that implanted medical devices are prone to bacterial adhesion and colonization on their surface. Implanted medical devices are also susceptible to thrombus formation and prion, blood protein and/or other protein formation.
Infections arising from the use of implanted medical devices, such as heart valves, stents, catheters, joint prostheses, intraocular lenses and dental implants etc. are associated with increased morbidity and mortality, prolonged hospitalisation, patient discomfort and increased medical costs. Progress in the area of anti-microbial treatment has been of limited success. For example, infection reportedly occurs in up to 13.9% of patients following stabilization of open fractures and in about 2% of patients who receive joint prostheses. Due to infection, prosthetic valve endocarditis remains one of the most dangerous and life-threatening complications following heart valve replacement. Mortality rates as high as 75% have been reported. Furthermore, urinary or vascular catheters are associated with a high rate of infection, about 7.6 infections per 1000 catheter-days.
Anti-microbial coatings for medical devices have recently emerged as a potentially effective method for preventing device-related infections. This is achieved by releasing anti-microbial agents from a coating to kill bacteria or to inhibit bacterial colonization. Some medical devices such as prosthetic heart valve sewing rings, stents, catheters and orthopaedic implants coated with anti-microbial agents have been reported. The anti-microbial agents used are silver, antibiotics combined with minocycline and rifampin, and surfactants etc. (Haley R W, “Estimating the Extra Charges and Prolongation of Hospitalisation Due to Nosocomial Infections: A Comparison of Methods”. J. Infect. Dis., 141:248-257 (1980); DiTizio V, Ferguson G W, Mittelman M W, Khoury A E, Bruce A W, DiCosmo F, “A Liposomal Hydrogel for the Prevention of Bacterial Adhesion to Catheters”, Biomaterials, 19:20, 1877-1884 (1998); Illingworth B L, Tweden K, Schroeder R E, Cameron J D, “In Vivo Efficacy of Silver-Coated (Silzone (TM)) Infection-Resistant Polyester Fabric Against a Biofilm-Producing Bacteria, Staphylococcus Epidermidis”, Journal Of Heart Valve Disease, 7: (5) 524-530 (1998); Stamm W E. “Catheter-Associated Urinary Tract Infections: Epidemiology, Pathogenesis, and Prevention”, Am. J. Med., 91:65-71 (1991); Darouiche, R O, “Prevention of Vascular Catheter-Related Infections”, The Netherlands Journal of Medicine 55:92-99 (1999)).
However, the currently available antimicrobial coatings have the problems of poor abrasion and poor corrosion resistance, limited biocompatibility and other adverse side effects. For example, the local cytotoxicity of silver-coated catheter cuffs and orthopaedic implants on human fibroblast cells has been observed.
Furthermore, there has been a growing understanding that the generation of wear debris due to friction at articulating surfaces or the release of metal ions can lead to severe cell response and bone resorption or osteolysis, giving rise to premature failure of implants.
Blood contacting devices often suffer from thrombus formation due to limited haemocompatibility. The interaction of an implanted material surface with blood stimulates platelet activation, leading to blood coagulation and thrombus formation. Numerous studies have been done to reduce thrombus formation by coating device surfaces with diamond-like carbon or bioactive materials. Diamond-like carbon shows great promise as a durable, wear- and corrosion-resistant coating for biomedical implants. Despite these favourable results and continuous technical improvements, the application of stents, artificial arteries and vascular catheters etc. is still limited by subacute occlusion and restenosis due to thrombus formation, especially in low flow and stagnation zones. The initial step of thrombus formation on blood-contacting biomaterials is known to be adsorption of blood proteins followed by platelet adhesion. However, diamond-like carbon coatings cannot inhibit blood protein adhesion to their surfaces significantly.
Cleaning, disinfection and sterilization of surgical instruments is crucial as they are in direct contact with blood and internal organs. It is critical that prior to any disinfection or sterilisation procedure that all items undergo a thorough physical cleaning. However, the stains on the surfaces of surgical devices from contamination are not easily removed. Prion (a microscopic protein particle similar to a virus but lacking nucleic acid, thought to be the infectious agent responsible for scrapie and certain other degenerative diseases of the nervous system) diseases constitute a unique infection control problem because prions exhibit unusual resistance to conventional chemical and physical decontamination methods. Recommendations to prevent cross-transmission of infection from medical devices contaminated by Creutzfeldt-Jakob disease (CJD) have been based primarily on prion inactivation studies. On the basis of the scientific data, only critical (e.g. surgical instruments) and semicritical devices contaminated with high-risk tissue (i.e. brain, spinal cord and eye tissue) from high-risk patients—those with known or suspected infection with CJD—require special treatment. The whole issue of contamination has become highly topical recently with concerns about the spread of CJD through surgical and butchers' instruments (e.g. knives). So far no attempts have been made to develop CJD-resistant surgical instruments.
It is an object of at least one aspect of the present invention to obviate/mitigate one or more of the aforementioned disadvantages.
It is a further object of the present invention to provide coatings with anti-microbial properties and/or improved haemocompatibility.
It is yet a further object of the present invention to provide a material which may be coated on a surface or substrate which is capable of inhibiting any of the following from adhering to surfaces: microorganisms, platelets, proteins (blood protein or prion protein) and/or cells.